Volume control



Noy. 1, 1949. A c. N. KIMBALL ETAL VOLUME CONTROL n Filed Feb.' s, 1946 INVENToR 5mm/r l?. 7311.552 .77.-

Patentedr ov. 949

'UNITE-o STATE-sf PAT oFifiC" Reconstliutionf-inance Grpo1fati'cn;.,.Kansas. City, M0., a corporation of the United States It is a'ri object of our invention to provide; for, a;4 loudispeakensuch a's al' speaker associated With"V a phonograph; radio' receiving set; o'r public address systemya volume" control means Which WilVoperate automatically to proportioispeaker 5 volume tov the,..intensity of sounds originating" from' sourcesgpther than the speaker. More specicallygit; is .0111" object. .to produce a control. means whicnjwillautomatically increaseoutput of they sigeaken upon .a'n increase in rthe intensity,y at nagdefii'-te Qontrol point,.,of sounds originating from'hl Siues- .AhQtrler object ofur in; veuticnis to. produce control means which will. fuuctiou-0nti1luouly While. .the speaker.. is. .in

' 10H., e'iuther-0biectl9f9urintentionistq.

Control ift/nichten .readily .be te@ wthepeaker and. itsassociatedamf piilnwthcut materially modifying' theconstrucr.

fen, W eroyifie metes-.Siruela for. @serate ing ari leneit, such as a pote.nti'oiirreter,.capableA Ecart A)Sinistrolliurel speaker-volume d an1 we ontrol eration notA connecte 1t l '.t such 1 alolrlaifatusA I, employ and Figlrz is anv elevatioii,

also somewhat diagrammatic in character, illus?. tratng' a suitable form of niotr-dr'iven' co`1`1t`1o'l` meansV` f r, l

In' Fig. .1. we haye illustrated portions of the" complete. apparatus as interconnected through, an. eight-contactjack oilsocket L0 andacdnpeitating' plug 5 1, asthen.apparatus.is prefei'ablysoearn ranged ini practice. `Inter'engaging" contacts, o1k the piue...l.tanl iaclielQLare showninFiei as comspoudinely positioned; and hereinafter,1.ex., cept as otherwise noted, itL/,ill be" assumed that theclugeudiacli areengaged: o.

@he -supalzatusmhich to. be. .automatically controlled ccmpriscs. arnatldiorfrenuency ampli.- @1f-15th@ .illllllllwit Qf. includes ap0ten--. tio??? Per., .lsilavine a inviable. contact .,|..1..,..`The. Detentiomcter ttiledeptcd to pcconnectedto. pho oaqtenh, pick-uml@ lf...to.-selxle.pther Saillies @trent-The paakemitthe lofil a 251,15 split ph thaw@ field. w...

to adjust potentiometer 26 to raise or lower speaker-volume. Operation of the motor is controlled by two relays and 36. To this end, one of two current-supply wires 4| and 42, shown as Ithe wire 4|, is connected to motor-terminal 32, While the other is connected through conductors 43 and 43 with the movable contacts of relays 35 and 36. Motor-terminal 33 is connected through conductors 44 and 44 with the fixed contact or relay 35, while conductors 45 and 45 interconnect motor-terminal 34 and the fixed contact of relay 36. Thus, by selective energization of the relays 35 and 36 the motor 25 can be caused to rotate in either direction.

The winding of relay 35, together with the grounded portion 56 of a voltage divider, is included in the plate circuit of a triode 5| the cathode of which is grounded. The winding oi the relay 36 and the other portion 52 of the voltage-divider are connected in the plate cir- L cuit of a second triode 53. The grid of triode 53 is connected to the plate of triode 5|.

Plate voltage for the triodes 5| and 53 is provided by a power-pack 55 having its positive highvoltage terminal connected by conductor 56 to l the ungrounded end of the voltage divider -52 and its negative high-voltage terminal grounded through a resistance 51. Low-voltage leads 58 from the power pack may be employed to supply current to cathode-heating laments (not shown) of the triodes 5I and 53 and of other electron discharge devices incorporated in the apparatus. Current for the power pack 55 is supplied through a conductor 59, connected to conductor 43', and conductors 60' and 60 exi..

tending to supply wire 4|.

The control grid of triode 5| is connected to a point .r between two resistances 6| and 62 connected in series with a rectier 63 so arranged that any current flowing in the circuit 63-82--6I will cause the potential at point to be negative with respect to that at point y at the opposite end of resistance 62. The circuit 63-62--6I is coupled, as by an audio-frequency transformer 64, with the output circuit of a voltage ampliiier 65 the input circuit of which is connected to a microphone 66 located at the desired control point. As a result, the current owing through the resistance 62, and hence the voltage drop across such resistance, will be generally proportional to the sound intensity at the microphone. The amplier 65 may include an adjustable element not shown) to control the gain it provides,

A resistance 61 has one terminal connected at the point y and its other terminal z connected to a resistance 68, and the two resistances 61 and 58 are connected in series with a rectifier 69 so arranged that the potential at y will be positive with respect to that at point z when direct current ilows through the circuit 69-68-61- Across the resistance 68 we impress an audio-frequency voltage proportional to the audio-frequency voltage impressed on the speaker 20 by the amplier I 5. To this end, the point z is grounded, through a condenser 1|, and the opposite terminal of resistance 68 is connected through a condenser 12, a potentiometer 13, and conductors 14 and 14 with the plate 15 of one of the tubes in the last stage of the amplifier l5. The -condenser 12 isolates the point 2 from the direct-current voltage maintained on the plate 15, while the condenser 1| isolates such point from ground, thus making it possible to control the potential at the point e by means hereinafter to be described. Obviously, the current traversing the resistance 61 and the voltage-drop across such resistance will vary in the same sense as does the audio-frequency voltage impressed on the speaker 20 by the amplifier l5. A condenser 16, connected between points .r and z, co-operates with the resistances 5|, 62, 61, and 68 to form a lter network which will compensate at least in part for audio-frequency iiuctuations.

Conductors 11' and 11 connect the point z with the movable contact 18 of a potentiometer 19 the terminals of which are connected respectively, through conductors 811-88 and 8|-8|, with the high-voltage terminals of the power pack 55. For a purpose which will hereinafter become apparent, the contact 18 is operated by the motor 25, conveniently by being mounted on a shaft 83 driven at reduced speed through a worm 84 and worm-gear 85 from the motor shaft 29.

Before proceeding with an explanation of the operation of the apparatus as a whole, it may be well to note the manner in which the energization of the relays 35 and 36 is controlled by the triodes 5| and 53. Since the control grid of triode 53 is negatively biased by the amount of the voltage drop across the winding of relay 35, since the current ilowing through such winding is controlled by the bias of the grid of triode 5|, and since the cathode of triode 5| is grounded, the potential at point x, to which the grid of triode 5| is connected, is the controlling factor in the operation of the relays 35 and 36. Normally, the bias of the grid of each triode will be such as will prevent the passage of suiiicient plate current to energize the associated relay. A drop in the potential at point if sufficient in extent, will decrease the current in the winding of relay 35 to a point such that the resultant reduction in the negative bias of the grid oi triode 53 will increase the plate current therethrough to a value great enough to energize relay 36. On the other hand, an increase in the potential at point :c will cause the triode 5| to increase the current traversing the winding of relay 35 and thereby to increase the negative bias of the grid of triode 53. If the increase in potential at point a: is suilicient, the relay 35 will be energized.

The potential at point :c is determined jointly by the potential at point z and the respective voltage drops across resistances 61 and 62. More specifically, the potential at will equal that at z plus the voltage drop from y to z minus the voltage drop from y to z. As long as the position of the microphone 66 is not changed, the current through resistance 61 and the voltagedrop from y to c will be generally proportional to the intensity of the sound received at the microphone from the speaker 20. The current through resistance 62 and. the voltage-drop from y to :c will be generally proportional to the aggregate of the intensities of all sounds received at the microphone. Accordingly, the potential dilerence between points a and a: will reiiect the intensity of sound received at the microphone from all sources other than the speaker 20, the potential at :c dropping with an increase and rising with a decrease in the intensity of such sounds.

In setting up the apparatusy the microphone 66 is located at the point where the desired control is to be exercised. With the speaker operating to produce sound of the desired intensity at the microphone, with no other sounds of material intensity reaching the microphone, and

With the movable contact 18 at or ucar the 10W- potential end f the potentiometer 18. the rotentiometer 'I3 is adjusted to vary the voltage-dl'OD across resistance 61 until the potential atx is at least roughly midway between the Value which results in enersization of the relay .85 and the value which results in energization or the relay 36. In this connection, it is to be noted that the presence of the resistance 51 in the ground lead to the negative terminal of the power-pack 55 makes it possible to bias the grid of triode l negatively relative to its associated, grounded cathode.

The apparatus, after being initially set up as above set forth, operates as follows:

As long as the sound intensity at the microphone from sources other than the speaker is not too great, the relays and 35 are open, the motor 25 is not running, and the potentiometer lli-I1, which controls speaker volume, remains in a xed condition of adjustment. As sound from sources other than the speaker increases, the potential at point and on the control grid of triode 5I decreases, thus decreasing the plate current, the voltage drop across the winding of relay 35, and the negative bias of the grid of triode 53. When the decrease in the negative grid-bias of triode 53 becomes sufficient, the relay 36 is energized to complete a circuit from supply wire 4l through terminals 32 and 34 of lmotor 25, conductors and 45', contacts of relay 36, and conductors 43 and 43 to the other supply wire 42. In the resultant operation of the motor, the contact I1 of potentiometer I6 is moved to increase the output of speaker 20. At

the same time, the motor moves contact 18 toward the high-voltage end of the potentiometer '19. The increase in the output of the speaker 20 will increase sound intensity at the microphone B6 to increase the current owing through the resistance 62, thus tending to lower still further the potential at x and on the grid of triode 5I; but this tendency is counteracted by the increase in the potential drop .from y to e which accompanies increased speaker output. As a result, the potential difference between points a: and e remains reasonably unaffected by variations in sound intensity at the microphone which result from changes in speaker output. However, as the potentiometer l6-I1 is adjusted by motor 25 to increase speaker output, the potentiometer-contact 18 is adjusted by the motor to raise the potential at point e, and thus. the potential at :c will be restored to the value at which relay 36 is cle-energized. When this occurs, the circuit through motor 2,5 is broken and the motor stops.

When the intensity of sound from sources other than the speaker decreases, the current through resistance 52 decreases to decrease the voltage drop from y to :c and raise the potential at If these changes are of sucient magnitude, the plate current through triode 5| becomes sufficient to energize relay 35 and complete a circuit from supply wire 4l, through motor 25 between terminals 32 and 33 thereof, conductors 44 and 44', contacts of relay 35, and conductors 43' and 43 to supply wire 42. This causes the motor 25 to adjust contact l1 of potentiometer I6 to reduce speaker output and contact 18 of potentiometer 19 to reduce the potential at point z. The resulting increases in the currents through resistances 62 and 61 and in the voltage drop across such resistances have opposite effects on the potential difference between points 1: and z, but the drop in potential at point z lowers the potential at .1: and

reduces the current traversins the winding of relay 35. This operation continues until the relay 35 becomes de-energized to interrupt the supply 0f current to the motor 25.

The constants of the system are preferably selected so that the contact -'I8 of potentiometer 'I9 may have imparted to it a potential which, if imposed on the grid of triode 5l, would maintain both relays 35 and 36 de-energized and so that the potential drop from y to will substantially equal that from y to a when no sound other than that originating from speaker 20 reaches the microphone 66. The resistances 6I, 62, 61, and 68 are so proportioned that a change in speaker output will produce substantially equal changes in the respective voltage drops across resistances 62 and 61. If the normal voltage-drop across the winding oi relay 35 is not of a magnitudo to produce the desired bias on the grid of triode 53 the leads from such relay-winding and the cathode of such triode, instead of being connected to the same point on the voltage divider 523-52, may be connected to different points thereon.

To facilitate the setting up of the apparatus, the amplier I5 may include any suitable form of adjustable element (not shown) for varying speaker volume independently of potentiometer Iii-l1. Also, one or both of the motor-operated contacts I1 and 'I8 may be adjustable on its driving shaft, or one or both of the annular resistance elements I6 and 19 may be mounted for adjustment about its axis, to vary the relation between the respective settings of the contacts l1 and 78.

If it should be desired to substitute manually operated control of speaker output for the automatic control provided by the apparatus connected to socket IIJ, I may employ a socket 9D which will receive plug H. and which, through conductors 44.", 43, and 45, will serve to connect the conductors 44, 43, and 4'5 respectively with, the movable contact and xed contacts ci a single-pole, double-throw switch 9i the movable contact of which is desirable biased to open position, By operation of the switch 9i, the supply wire 42 may be connected to either terminal 33 or 34 of the motor 25, thus making it possible to Cause the motor to move the contact l1 of potentiometer I6 and lower or raise speaker volume.

We claim as our invention:

1. In combination with an electrically operated, sound-emitting speak-er, means for supplying an audio-frequency current thereto, two series-.connected resistances, means for creating through one of said, resistances a direct current which nov/s from the. point of. interconnection of the resistances and which varies in the same sense as does the audio-frequency current supplied to said speaker, means for creating through the other of said resistances a direct current which flows from the point of interconnection of the resistance and which varies in the same sense as does the intensity of sound at a predetermined control point, and means responsive to the potential difference across both resistances for controlling the audio-frequency current supplied to the speaker.

2. In combination with an electrically operated, sound-emitting speaker, means for supplying an audio-frequency current thereto, two electrical circuits, means for creating in one of said circuits an electric current which varies in the same sense as the audio-frequency current supplied to the speaker, means for creating in the other circuit an electric current which varies in the same sense as does the intensity of sound at a predetermined control point, and means controlled jointly by the currents in said two circuits for varying the audio-frequency current supplied to the speaker.

3. In combination with an electrically operated, sound-emitting speaker, means for supplying an audio-frequency current thereto, soundresponsive means located at a predetermined control point, means controlled jointly by said sound-responsive means and by the audio-frequency current supplied to said speaker for varying said audio-frequency current.

4. In combination with an electrically operated, sound-emitting speaker, means for supplying an audio-frequency current thereto, and automatic control apparatus for varying said audio-frequency current, said control apparatus including a resistance, means for creating across said resistance a potential-difference responsive to the intensity of sound received at a predetermined control point from sources other than said speaker, means for imposing on one terminal of said resistance a potential proportioned to the current supplied said speaker, and means responsive to the potential at the other terminal of said resistance for controlling said speakercurrent.

5. In combination with a loud speaker, an adjustable device for varying the volumes of said speaker, a reversible electric motor for operating said device, and means responsive to the intensity of sound received at a predetermined control point from sources other than said speaker for selectively controlling said motor.

6. In combination, first and second electron discharge devices each having an anode, a cathode, and a control element, a first plate circuit including the anode and cathode of said first device and the winding of a first relay, a second plate circuit including the anode and cathode of said second device and the winding of a second relay, a grid circuit including the cathode and control element of said first device, and a grid circuit including the cathode and control element of Said second device, said second grid circuit also including the winding of said first relay so connected in said second grid circuit that an increase in the current flowing in the first plate circuit will reduce the potential of the control element of the second device.

'7. In combination, rst and second electron discharge devices each having an anode, a cathode, and a control element, a first plate circuit including the anode and cathode of said first device and the winding of a iirst relay, a second plate circuity including the anode and cathode 8. In combination, first and second electron discharge devices, each having an anode, a cathode, and a control element, a first plate circuit including the anode and cathode of said first device, a second plate circuit including the anode and cathode of said second device, means for imposing a variable potential on the control element of the first device, and means responsive to the value of current iiowing in said first plate circuit for varying the potential of the control element of the second device in a sense opposite to that in which said plate current varies.

9. In combination, first and second electron discharge devices each having an anode, a cathode, and a control element, a first plate circuit including the anode and cathode of said first device, a second plate circuit including the anode and cathode of said second device, means for imposing a variable potential on the control element of the first device, and means responsive to the value of current ilowing in said first plate circuit for varying the potential of the control element of the second device.

10. The invention set forth in claim '7 with the addition of a translating device selectively controllable by said relays.

11. A method of controlling the volume of an electrically operated, sound-emitting speaker, which comprises controlling current supplied to said speaker in accordance with the difference of potential between two points in an electric circuit and automatically varying such potential difference in accordance with the difference between the intensity of sounds received from all sources at a predetermined control point and the intensity of sound received from said speaker at such control point.

CHARLES N. KIMBALL. BEN E. BROWN. SIMEON R. TYLER, Jn.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,607,673 Inglis Nov. 23, 1926 2,338,551 Stanko Jan. 4, 1944 2,382,848 Baumgartner Aug. 14, 1945 2,392,218 Anderson Jan. 1, 1946 2,420,933 Crawford Mar. 20, 1947 

